A cellular communication system can support bi-directional communication for multiple users by sharing the available system resources. Cellular systems are different from broadcast systems that can mainly or only support unidirectional transmission from broadcast stations to users. Cellular systems are widely deployed to provide various communication services and may be multiple-access systems such as Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal FDMA (OFDMA) systems, Single-Carrier FDMA (SC-FDMA) systems, etc.
A cellular system may support broadcast, multicast, and unicast services. A broadcast service is a service that may be received by all users (e.g., a news broadcast). A multicast service is a service that may be received by a group of users (e.g., a subscription video service). A unicast service is a service intended for a specific user (e.g., a voice call). Group communications can be implemented using either unicast, broadcast, multicast, or combinations thereof. As the group becomes larger, using multicast services may generally be more efficient. However, for group communication services that require low latency and a short time to establish the group communication, the setup time of conventional multicast channels can be a detriment to performance.
For example, to provide large group call services in dense user areas according to the evolved multimedia broadcast/multicast services (eMBMS) standard, the bearers for multicast calls are typically established statically or semi-statically (i.e., the bearers need to be established before the call starts). Consequently, the target area associated with a multicast call has to be identified, the network components have to be connected, and the group member list needs to be pre-provisioned before the call starts, which tends to results in a static group experience. Furthermore, when a group call crosses home network boundaries due to user mobility, there may be a need to provide service in roaming networks (e.g., visited networks). However, the services provided under the current eMBMS standard are not designed to provide seamless operation in roaming scenarios. Instead, services currently provided under the existing eMBMS standard are generally designed to terminate when home network boundaries are crossed. Moreover, no group calling services currently exist on the eMBMS standard except for the current proposals in 3GPP Release 12 specifications for group communication, specifically for critical communication services.